Lecture 16 Transposable elements

Question 1

Transposition
(meaning)

Answer 1

Movement of a segment of DNA (transposable elements/transposon) from one location to another.

Question 2

Transposable elements in corn: As and Ds
Ds =
Ac =
Autonomous elements encode information ____
→ Ac ~ Ds

Phenotypes caused by the As and Ds elements
Pigmented
(2 scenarios)

Colorless
(1 scenario)

Fully pigmented to some part unpigmented ()
(2 scenarios)

Colorless to spotted ()
(2 scenarios)

Mechanism of transposition in corn (DNA transposon)

Answer 2

Ds = nonautonomous element
Ac = autonomous element
Autonomous elements encode information required for their own movement and for the movement of nonautonomous elements.
→ Ac activates the excision of Ds

Phenotypes caused by the As and Ds elements
Pigmented (wild type)
C gene (wild type)/C Ds

Colorless
Cm(Ds)

Fully pigmented to some part unpigmented.
Chromosome breakage
→ C Ds (+Ac)/C Ac

Colorless to spotted
Unstable alleles
→ Cm(Ds) (+Ac)/Cm(Ac)

Mechanism of transposition in corn
Transposase binds to the repeated sequences at the ends of the transposable elements (Ac and Dc)
→ Cleavage
→ Integration into new target site
→ Transposable elements (Ac and Dc) at new location

Question 3

Classes of transposable elements in eukaryotes
all transposons are flanked by repeated sequences.

Retrotransposon
DNA to RNA (what element) to enzyme
(the original transposon?)
DNA transposon
DNA to RNA (what element) to enzyme to DNA repair at the cut)
(the original transposon?)
note: both transposons have repeated sequences

Answer 3

Retrotransposon “copy and paste”
→ Retrotransposon DNA transcribed to RNA by RNA polymerase
→ RNA (transcribed from pol gene) translated to reverse transcriptase and integrase
→ Reverse transcriptase reverse transcribes RNA to complementary DNA
→ integrase integrates DNA into a new location
the original transposon persists.

DNA transposon “cut and paste”
Transposon DNA transcribed to RNA by RNA polymerase
→ RNA translated to Transposase
→ Transposase binds and cuts the DNA transposon (P element) out of its original location and transports it to a new location.

→ Repair of DNA using a sister chromatid/homologous chromosome containing P element as template
the original transposon persists.
Or → Repair of DNA using a sister chromatid/homologous chromosome not containing P element as template
the original transposon deleted.